“…The weighted factor is referred as the credibility factor. Some historical references on this topic are Whitney (1918), Mowbray (1914), Bailey (1945), Bühlmann (1967), Kahn (1975), Gerber and Arbor (1980), Eichenauer et al (1988), Heilmann (1989), Goovaerts et al (1990) and Herzog (1996). For a recent revision of the credibility theory see Makov (1999, 2000), Promislow and Young (2000), Young (2000) and Gómez et al (2006).…”